Here is the way to recharge your dig cam batteries on a wilderness hike.
"Carrying weights of between 44 and 84 lbs, testers generated up to 7.4W,..."

The only problem is that I have a hard time imagining a nerd managing to carry 44 to 84 lbs of anything in a backpack! That would require some level of physical fitness. Neat concept though. I wonder if the motion causes any chafing?